Heading into this weekend’s referendum on Catalan independence, the Spanish authorities had everything going for them. The Spanish Constitutional Court had pronounced the referendum illegal, a straightforward violation of the 1978 constitution’s commitment to an indissoluble union of Spain’s nationalities. A substantial majority of residents of Catalonia opposed independence, according to most polling. A previous referendum in 2014 had achieved only 40 percent turnout, confirming local lack of interest.

The local government had pushed through a referendum law on the thinnest margin in the legislature, based its campaign on the false claim that an independent Catalonia would rapidly and easily be admitted to the European Union, and had committed to declare independence unilaterally if it obtained a “Yes” majority. The lesson from the U.K. that “exit” is never as easy as its proponents promise chastened many minds in Catalonia, which may explain why support for independence seemed to be ebbing.

Or the ebb may have been due to Spain’s gradual recovery from the economic crisis of 2010. Catalonia, with only 16 percent of the population but 19 percent of the economy, has long chafed at seeing its tax payments redirected to poorer regions. But Spain grew 3.2 percent in 2016, one of the fastest expansions in the whole eurozone. What looked for half a decade like a bad bargain had regained some of its prior attractiveness.

Until Sunday. It’s too early to assess the effect on Catalan opinion of the Spanish government’s heavy-handed response to the independence vote. Some protesters acted provocatively: The notorious firing of rubber bullets occurred as protesters sought to impede police movements. On the other hand, the police were moving to snatch ballot boxes away from polling stations, behavior that was provocative in its own right.

National examples are difficult to emulate across borders, but Spain may have something here to learn from the Canadian precedent of 1980-1995. Over those 15 years, Canada faced two secession referendums in Quebec. Unlike Catalonia, Quebec is poorer than the rest of its country; nor has Quebec experienced anything like Catalonia’s level of cultural suppression. (Over 150 years of confederation, a Quebecker has held Canada’s prime ministership for 67 years all told, the first time as long ago as 1896.) On the other hand, Quebec is a bigger piece of real estate and generally a more plausible candidate for independent statehood.

Quebec nationalism was seen off by many factors, but high on the list was the steady process of peaceful education about just how intractable, complicated, and expensive it is to divide a modern welfare state. Just one problem: Spain owes about a trillion euros in debt. How is that to be apportioned? Does Catalonia owe its 16 percent population share or its 19 percent economic share? And what about all the pensions? “The trouble with socialism is that it takes too many evenings,” Oscar Wilde is supposed to have said. If only he had encountered the fiscal consequences of separation...

But the precondition for this kind of “make it boring” strategy against secession is that it requires an absolute prohibition on state repression or violence against secessionists. Canada recognized that truth. So did the United Kingdom in its dealings with the Scottish Nationalists. Violence inflames passions—and passion is exactly what is wanted by those with the weaker argument. In a modern democratic welfare state, the secessionists almost always have the weaker argument, because the costs and risks of change are certainly higher than those of a decent and reasonable status quo. So the secessionists seek to incite. In Catalonia, they succeeded, and all of Europe and Europe’s allies has to worry about the consequences that will follow.

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David Frum is a senior editor at The Atlantic. In 2001–02, he was a speechwriter for President George W. Bush.